The present invention relates to a friction disc for clutches and the like and more particularly to a friction disc having an improved configuration for reducing clutch drag losses.
It is well known that certain clutch discs, particularly those subjected to severe energy absorption levels, require cooling and lubrication during the engagement or disengagement of the clutch. This is particularly true of multi-disc clutches such as that shown in U.S. Pat. No. 2,690,248 to McDowall, issued Sept. 28, 1954. Considerable research effort has been expended in determining optimum configurations for clutch discs and lubrication systems therefor, as exemplified by U.S. Pat. Nos. 2,020,748; 2,556,809; 3,347,345; and 3,412,836. However, there is still room for additional improvement.
In general, two main factors are involved and these factors include the clutch drag losses for different disc groove patterns and cooling of the friction surfaces. Spiral and radial groove patterns for distributing cooling oil have been in use since the introduction of power shift transmission clutches and most of those used today have both types of grooves. Spiral groove patterns have the disadvantage of developing relatively high drag losses whereas discs with diamond or sunburst groove patterns operate at the lower drag levels. However, ineffective oil cooling shortens the life of friction materials that operate at high energy levels, and the grooving employed effects the cooling as well as the frictional drag losses. Since the transmission art is toward the use of higher speeds and loads, the discs employed must handle more energy, last longer, be more reliable, and in some cases require less space with reduced drag losses. Accordingly, the present invention is directed to a special disc configuration which effects an improvement in this area.